1. Field of the Invention
The present invention relates to a hydrodynamic bearing spindle motor suitable for use in a hard disk or the like used for a personal computer and various audio-visual appliances.
2. Description of the Prior Art
FIG. 2 shows a hydrodynamic bearing spindle motor for use in a known hard disk. In the known hydrodynamic bearing spindle motor of FIG. 2, a base 1 has radial bearing portions 1a and acts as a fixed member. A rotary shaft 2 is secured to a flange 4 so as to be rotated together with the flange 4 and is rotatably supported by the radial bearing portions 1a of the base 1 and a thrust bearing 9 so as to be smoothly rotated at high speed. Lubricant 3 is provided in a clearance between the radial bearing portions 1a and the rotary shaft 2 and oil having a predetermined viscosity is usually employed as the lubricant 3. A plurality of, for example, four disks 5 are mounted on an outer periphery of the flange 4 in parallel with each other and the flange 4 is coaxially fixed to the rotary shaft 2 so as to act as a rotational member. Each of the disks 5 is constituted by a magnetic disk used generally for a hard disk of a personal computer. A coil 6 is fixed to the base 1, while a magnet 7 is attached to the flange 4 so as to confront the coil 6. By effecting flow of electric current through the coil 6, rotational force is generated between the coil 6 and the magnet 7 and thus, the flange 4 can be rotated at high speed. A clearance 8 is formed between the base 1 and the flange 4. The thrust bearing 9 is secured to the base 1 so as to bear thrust load of the rotary shaft 2.
Operation of the known hydrodynamic bearing spindle motor of the above described arrangement is described below. By effecting flow of electric current through the coil 6, rotational force is generated between the coil 6 and the magnet 7 and thus, the flange 4 having the disks 5 mounted thereon is rotated together with the magnet 7 at high speed. Therefore, information signals such as image and sound signals and text data are recorded on the disks 5 by a magnetic head (not shown). Meanwhile, if the information signals have been recorded on the disks 5, the information signals can be reproduced on the disks 5 by the magnetic head.
Since the lubricant 3 is provided between the rotary shaft 2 and the radial bearing portions la as described above, the flange 4 secured to the rotary shaft 2 can be rotated at high speed smoothly. Meanwhile, lubricant (not shown) is provided also between the rotary shaft 2 and the thrust bearing 9 so as to serve to bear thrust load of the rotary shaft 2 smoothly.
However, in the known hydrodynamic bearing spindle motor, the lubricant 3 provided in the clearance between the radial bearing portions 1a and the rotary shaft 2 leaks out of the radial bearing portions 1a due to impact caused by fall of the known hydrodynamic bearing spindle motor, etc. and is carried through the clearance 8 between the flange 4 and the base 1 by centrifugal force due to high-speed rotation of the flange 4 so as to finally adhere to the disks 5. If the lubricant 3 has adhered to the disks 5 as described above, such an inconvenience is incurred that the recording head cannot properly record and reproduce the image and sound signals, etc. on the disks 5.